I kinda prefer the R&D design because it's longer & the flange gives you port matched air flow from the throttle body to the manifold. The pics below are from a SHO manifold. The throttle body mounts in a different spot on the VXR, but the mount is the same. You can see how the R&D(silver one) keeps a smooth ID through the TB bracket, while the Riva(black one) doesn't extend past the manifold. Not sure if it makes much difference but every little bit helps on a NA motor.

your right, but its for the SHO/FZ, i'm picking up a FXS, its a $49.95 piece for the metal one............ different pn as well, but i can see how the metal piece fits better, worth the extra ten bucks m sure

I personally use the Riva one. Works fine, I don't see how any of the various manifold upgrades are better than the other. The install is pretty straight forward too, despite what others may say. Pull the fuel rail, electricial connectors, manifold, and install. Get your hands on a service manual for torque specs, tips, etc for the install. Well worth the 70$ price tag.... or find someone with a PDF for free.